13 - 19 Flashcards
What are the main functions of the cardiovascular system?
It delivers oxygen and nutrients to tissues, removes carbon dioxide and metabolic waste, transports hormones, and helps maintain homeostasis.
How much blood does the human heart pump per minute?
Each side of the heart pumps 5 litres per minute, delivering ~250 mL of oxygen and removing ~200 mL of carbon dioxide.
What are the four chambers of the heart, and what do they do?
Right atrium (RA): Receives deoxygenated blood from the body.
Right ventricle (RV): Pumps deoxygenated blood to the lungs.
Left atrium (LA): Receives oxygenated blood from the lungs.
Left ventricle (LV): Pumps oxygenated blood to the body.
How do the heart valves control blood flow?
Tricuspid valve: Between RA and RV, opens in diastole.
Pulmonary valve: Between RV and pulmonary artery, opens in systole.
Mitral (bicuspid) valve: Between LA and LV, opens in diastole.
Aortic valve: Between LV and aorta, opens in systole.
What are the two circulatory systems in the body?
Systemic circulation: Oxygenated blood from the left heart to the body.
Pulmonary circulation: Deoxygenated blood from the right heart to the lungs.
What is systole and diastole?
Systole: Ventricular contraction, ejecting ~70 mL of blood. (~300 ms)
Diastole: Ventricular relaxation, allowing the heart to fill. (~550 ms)
What causes heart sounds?
“Lub” (S1): Mitral and tricuspid valves closing in systole.
“Dub” (S2): Aortic and pulmonary valves closing in diastole.
What is cardiac output, and how is it calculated?
Cardiac output (CO) = Stroke volume × Heart rate.
At rest:
Heart rate ≈ 70 bpm
Stroke volume ≈ 70 mL
CO ≈ 5 L/min
What is Starling’s Law of the Heart?
The energy of contraction is proportional to the initial stretch of cardiac muscle fibres, ensuring equal blood output from both sides of the heart.
What is the conduction pathway of the heart?
Sinoatrial (SA) node: Pacemaker, starts impulse.
Atrioventricular (AV) node: Delays impulse.
Bundle of His: Conducts to ventricles.
Purkinje fibres: Spread impulse across ventricles.
How does the sinoatrial (SA) node generate pacemaker potential?
By gradual Na⁺ and Ca²⁺ influx and reduced K⁺ efflux, leading to depolarisation.
What are the phases of a ventricular action potential?
Phase 0: Rapid Na⁺ influx (depolarisation).
Phase 1: Short K⁺ efflux (partial repolarisation).
Phase 2: Ca²⁺ influx (plateau phase).
Phase 3: K⁺ efflux (repolarisation).
Phase 4: Resting potential.
Why does cardiac muscle have a long refractory period?
To prevent tetanus, ensuring proper filling and contraction cycles.
What is the role of intercalated disks in cardiac muscle?
They contain gap junctions, allowing electrical signals to rapidly pass between cardiac cells, enabling synchronous contraction.
What information does an ECG provide?
It records the electrical activity of the heart, diagnosing arrhythmias, heart attacks, and conduction defects.
What are the two main circulatory systems in the human body?
Systemic circulation – Carries oxygenated blood from the left ventricle to the body and returns deoxygenated blood to the right atrium.
Pulmonary circulation – Carries deoxygenated blood from the right ventricle to the lungs for oxygenation and returns it to the left atrium.
How do blood vessels accommodate different pressures in circulation?
Arteries handle high pressure (~100 mmHg).
Veins operate under low pressure (0–8 mmHg) and act as blood reservoirs.
Capillaries facilitate exchange and maintain equilibrium.
What are the three main layers of blood vessel structure?
Tunica intima – Endothelium + connective tissue (releases paracrine signals).
Tunica media – Smooth muscle + elastic tissue (controls vessel diameter).
Tunica adventitia – Collagen-rich outer layer (provides structure).
What is the Windkessel effect, and why is it important?
The Windkessel effect occurs when elastic arteries store energy during systole and release it during diastole, maintaining continuous blood flow.
What role do muscular arteries play in circulation?
Muscular arteries control blood flow resistance by adjusting their diameter via smooth muscle contraction.
What three factors determine blood vessel resistance?
Length of blood vessels (longer vessels increase resistance).
Blood viscosity (thicker blood increases resistance).
Radius of blood vessels (a smaller radius dramatically increases resistance).
How does Poiseuille’s Law describe blood flow resistance?
Resistance (R) is inversely proportional to the radius⁴:
If the vessel radius is halved, resistance increases 16-fold, drastically reducing flow.
What is the difference between laminar flow and turbulent flow in blood vessels?
Laminar flow – Blood moves in smooth layers, reducing resistance.
Turbulent flow – Blood moves chaotically, increasing resistance and leading to potential arterial damage.
What are the primary functions of capillaries?
Gas exchange (O₂ & CO₂ diffusion).
Nutrient & waste exchange.
Fluid equilibrium between plasma & interstitial fluid.
How do lipid-soluble and water-soluble molecules cross capillary walls?
Lipid-soluble molecules (O₂ & CO₂) diffuse directly through capillary membranes.
Water-soluble molecules (glucose & ions) pass through pores or intercellular clefts.
What are Starling forces, and how do they regulate capillary exchange?
Hydrostatic pressure (35 mmHg at arteriole, 15 mmHg at venule) pushes fluid out of capillaries.
Oncotic (colloid osmotic) pressure (25 mmHg) pulls fluid back in.
The balance of these forces determines filtration or reabsorption.
What happens to excess fluid that is not reabsorbed in capillaries?
Excess fluid is taken up by the lymphatic system, which returns it to circulation and samples it for immune surveillance.
How do veins function as capacitance vessels?
Veins store ~3.3 litres of blood that can be mobilized during exercise or blood loss to maintain circulation.
What mechanisms assist venous return to the heart?
Muscle pump – Skeletal muscle contractions squeeze veins.
Respiratory pump – Inhalation reduces thoracic pressure, drawing blood toward the heart.
Venous valves – Prevent backflow of blood.
How does postural hypotension occur?
Standing quickly can cause blood pooling in the veins, reducing venous return and cardiac output, leading to a temporary drop in blood pressure.
How does the autonomic nervous system (ANS) regulate the heart?
Sympathetic nervous system (SNS): Increases heart rate and contractility via noradrenaline (NA).
Parasympathetic nervous system (PNS): Decreases heart rate via acetylcholine (ACh).
How does the ANS affect blood vessels?
Only the sympathetic nervous system innervates blood vessels.
Noradrenaline (NA) causes vasoconstriction, increasing resistance and venous return.
What is the role of the sinoatrial (SA) node in cardiac regulation?
The SA node is the heart’s primary pacemaker, setting the heart rate and responding to autonomic inputs.
What are chronotropic effects?
Positive chronotropic effect (SNS) = Increases heart rate.
Negative chronotropic effect (PNS) = Decreases heart rate.
What are dromotropic effects?
Positive dromotropic effect (SNS) = Increases conduction speed through the AV node.
Negative dromotropic effect (PNS) = Decreases conduction speed through the AV node.
What is an inotropic effect, and which system controls it?
Inotropic effects refer to changes in contractility.
Only the sympathetic nervous system affects contractility (positive inotropic effect via Ca²⁺ release).
How does the sympathetic nervous system affect Starling’s Law of the Heart?
The SNS increases contractility, enhancing stroke volume at any given filling pressure.
What are the main determinants of blood pressure (BP)?
Cardiac output (CO) = Heart rate × Stroke volume
Total peripheral resistance (TPR) = Controlled by arteriole diameter
Blood volume = Affected by kidney function and hormones
How does the baroreceptor reflex regulate blood pressure?
Low BP → Baroreceptors decrease firing → SNS activation → Increased heart rate & vasoconstriction.
High BP → Baroreceptors increase firing → PNS activation → Decreased heart rate & vasodilation.
What is the role of renin-angiotensin-aldosterone system (RAAS) in BP regulation?
Renin (from kidney) → Produces angiotensin II (vasoconstrictor).
Angiotensin II stimulates aldosterone, increasing Na⁺ and water retention, raising blood volume.
What do atrial stretch receptors regulate?
Detect increased blood volume and signal the hypothalamus to reduce ADH secretion.
Promote sodium excretion (ANP release), lowering extracellular fluid volume.
How do metabolites regulate local blood flow?
Adenosine & K⁺ cause vasodilation to increase blood flow to active tissues.
Myogenic responses & endothelial factors (e.g., NO) also influence vessel diameter.
What makes the pulmonary circulation unique?
Low resistance & high compliance (thin-walled vessels, large diameters).
Prevents pulmonary edema by maintaining low hydrostatic pressure.
How does oxygen regulate pulmonary blood flow?
Low oxygen (hypoxia) causes pulmonary vasoconstriction to direct blood away from poorly ventilated areas.
Opposite effect occurs in systemic circulation, where hypoxia causes vasodilation.
What happens in pulmonary hypertension?
Chronic hypoxia leads to persistent vasoconstriction and increased pulmonary artery pressure.
Can result in right heart failure if severe.
What are the primary physiological responses to haemorrhage?
Respond to blood volume reduction
Maintain blood pressure and cardiac output
Restore circulating fluid volume
How does haemorrhage initially affect blood pressure and cardiac output?
A fall in blood volume reduces venous return, leading to a drop in cardiac output and arterial pressure.
How does the baroreceptor reflex help correct blood pressure after haemorrhage?
Increases sympathetic drive → raises heart rate and contractility.
Arteriole constriction → increases total peripheral resistance (TPR).
Venous constriction → improves venous return.
What happens to capillary fluid exchange during haemorrhage?
Hydrostatic pressure falls, favoring fluid reabsorption into the circulation.
Helps partially restore blood volume but at the expense of increased viscosity.
What role does renin-angiotensin-aldosterone system (RAAS) play in haemorrhage compensation?
Renin secretion increases due to low kidney perfusion.
Produces angiotensin II, which vasoconstricts arteries and veins.
Aldosterone increases Na⁺ and water retention, restoring extracellular fluid volume.
How does erythropoietin (EPO) contribute to recovery after haemorrhage?
EPO stimulates red blood cell production, correcting for lost haemoglobin and oxygen-carrying capacity.
What are the four classes of haemorrhage, and how do they differ?
Class I (<15%): No significant symptoms.
Class II (15-30%): Tachycardia, pale skin, narrowed pulse pressure.
Class III (30-40%): Hypotension, shock, mental status deterioration.
Class IV (>40%): Severe shock, requires immediate resuscitation.
What are the key clinical treatments for severe haemorrhage?
Stop the bleeding (surgical intervention if needed).
Fluid resuscitation (blood transfusion, saline, or colloid).
Monitor oxygen levels (oximetry).
Monitor heart filling pressure (catheter in severe cases).
How does the cardiovascular system respond to exercise?
Increased cardiac output (CO) to supply skeletal muscles.
Redistribution of blood flow from less active organs to muscles.
Increased coronary blood flow to meet heart’s oxygen demand.
How does vasodilation in skeletal muscles occur during exercise?
Adrenaline acts on β₂ receptors, causing vasodilation.
Local metabolites (K⁺, adenosine, lactate) promote vasodilation.
How does sympathetic activation affect blood flow during exercise?
Vasoconstriction occurs in less active organs (GI tract, skin) via α-receptors.
Vasodilation occurs in muscles via β₂-receptors.
What prevents excessive cardiac filling during exercise?
Increased heart rate shortens diastole, limiting excessive filling.
Prevents overstretching of cardiac muscle.
How does Starling’s Law apply to exercise?
Increased venous return enhances stroke volume.
However, at high filling pressures, stroke volume stops increasing.
Why is cutaneous vasodilation important during exercise?
Helps with heat dissipation through sweating.
However, excessive vasodilation may divert blood from muscles, leading to heat stroke.
How does coronary circulation change during exercise?
Blood flow occurs mostly in diastole (systole compresses coronary vessels).
Adenosine release ensures coronary vasodilation to meet oxygen demand.
What is the difference between breathing and ventilation?
Breathing is the contraction/relaxation of respiratory muscles.
Ventilation is the movement of air into and out of the lungs for gas exchange.
What are the three aspects of central control of breathing?
Reflex/automatic control – Regulates breathing rhythm.
Voluntary/behavioural control – Conscious control from the motor cortex.
Emotional control – Breathing changes due to emotions (e.g., fear, anxiety).
Which brainstem regions generate respiratory rhythm?
Inspiratory rhythm – Generated by the preBötzinger Complex (preBötC).
Expiratory rhythm – Generated by the parafacial respiratory group.
What is the role of the motor cortex in breathing?
It allows voluntary control of breathing, overriding automatic rhythms when needed (e.g., breath-holding).
What is the “breaking point” for voluntary breath-holding?
When CO₂ levels rise too high or H⁺ concentration increases, overriding voluntary control and forcing inhalation.
How does emotional control influence breathing?
Fear/anxiety can alter breathing patterns.
Emotional control of breathing is preserved in locked-in syndrome, while voluntary control is lost.
What are the main chemoreceptors involved in respiratory control?
Peripheral chemoreceptors – Located in carotid and aortic bodies, detect low O₂ and high CO₂/H⁺.
Central chemoreceptors – Located in the medulla, primarily detect high CO₂ in cerebrospinal fluid.
How does hypercapnia (high CO₂) affect breathing?
Small CO₂ increases can double breathing rate.
10% rise in CO₂ → 100% increase in breathing.
20% rise in CO₂ → Breathing triples.
How does hypoxia (low O₂) affect breathing?
Less sensitive than CO₂ regulation.
A 35% drop in O₂ increases breathing by 20%.
A 55% drop in O₂ doubles breathing rate.
What is the role of pulmonary stretch receptors?
Slowly adapting receptors detect lung inflation, triggering the Hering-Breuer reflex to prevent overinflation.
Rapidly adapting receptors respond to irritants, triggering coughing, sneezing, and sighing.
What is the function of pulmonary surfactant?
Reduces surface tension in the alveoli, making lung expansion easier.
Secreted by Type II alveolar cells, especially during sighing.
Deficiency in premature babies causes respiratory distress syndrome.
How do cough and sneeze reflexes protect the respiratory system?
Coughing clears the upper airway, expelling air at 960 km/h.
Sneezing clears nasal passages, expelling air at 160 km/h.
How do the lungs regulate blood gases and blood pressure together?
Baroreceptors and chemoreceptors work together to balance oxygen (O₂), carbon dioxide (CO₂), and blood pressure through integrated neural circuits.
What happens to the respiratory system during exercise?
Increased ventilation due to rising CO₂ and H⁺ levels.
Activation of chemoreceptors and proprioceptors (muscle movement sensors).
What is the Hering-Breuer reflex, and why is it important?
A protective reflex that inhibits inspiration when the lungs are overinflated.
Prevents excessive lung expansion and potential damage.
What is the difference between breathing and ventilation?
Breathing is the physical act of air movement in and out of the lungs.
Ventilation refers to the process of gas exchange between the lungs and blood.
What are the three phases of rhythmic breathing?
Inspiration – Active contraction of inspiratory muscles.
Post-inspiration – Controls airflow and slows diaphragm recoil.
Expiration – Passive lung recoil or active expiratory muscle contraction.
Which muscles are involved in inspiration?
Diaphragm (main inspiratory muscle).
External intercostals (expand the ribcage).
Sternocleidomastoid & scalenes (assist in deep breaths).
Which muscles are involved in active expiration?
Internal intercostals (pull ribs down).
Abdominal muscles (obliques, transverse abdominis) increase pressure to push air out.
What is the pleura, and why is it important?
The pleura consists of two layers:
Visceral pleura (covers lungs).
Parietal pleura (lines thoracic cavity).
The pleural cavity contains fluid, creating a vacuum that keeps the lungs expanded.
What is transpulmonary pressure (Ptp), and how is it calculated?
Ptp = Palv – Pip (alveolar pressure minus intrapleural pressure).
It keeps the lungs inflated by preventing collapse.
What causes a pneumothorax (collapsed lung)?
Air enters the pleural cavity, eliminating the negative pressure.
This leads to lung collapse due to elastic recoil.
How does Boyle’s Law relate to breathing?
Boyle’s Law states: P1V1 = P2V2.
As lung volume increases, pressure decreases, drawing air in (inspiration).
As lung volume decreases, pressure increases, pushing air out (expiration).
What is Dalton’s Law, and how does it apply to gas exchange?
Dalton’s Law states that total pressure is the sum of partial pressures of individual gases.
Oxygen and CO₂ diffuse based on partial pressure gradients.
What is dead space, and what are its two types?
Anatomical dead space – Air in conducting airways (no gas exchange).
Physiological dead space – Air in alveoli that do not participate in gas exchange.
How is oxygen transported in the blood?
98% bound to haemoglobin.
2% dissolved in plasma.
What is the Bohr Effect, and why is it important?
CO₂ and acidity cause haemoglobin to release O₂ in tissues.
This ensures oxygen delivery to metabolically active tissues.
How is carbon dioxide (CO₂) transported in the blood?
70% as bicarbonate (HCO₃⁻) via carbonic anhydrase.
20% bound to haemoglobin as carbaminohaemoglobin.
5-10% dissolved in plasma.
What happens in carbon monoxide poisoning?
CO binds haemoglobin 210x stronger than O₂, forming carboxyhaemoglobin.
This prevents O₂ binding and release, leading to tissue hypoxia.
How does respiratory quotient (RQ) affect gas exchange?
RQ = CO₂ produced / O₂ consumed (normally 0.7–1.0).
It affects alveolar gas calculations and respiratory efficiency.
What are the main divisions of the respiratory system?
The respiratory system is divided into the upper airways, lower airways, conducting zone, and respiratory zone.
What structures are part of the upper respiratory tract?
The mouth, nose, pharynx, and larynx.
What is the primary function of the conducting zone?
To conduct air from the mouth and nose to the terminal bronchioles without gas exchange, while moistening and defending against microbes.
What happens in the respiratory zone?
It is the site of gas exchange, where oxygen is taken in and carbon dioxide is expelled.
How many lobes are there in each lung?
The right lung has three lobes, and the left lung has two lobes.
What is the “mucus escalator”?
A defense mechanism where cilia move mucus and trapped particles upward toward the pharynx to be swallowed.
What are alveoli, and why are they important?
Small air sacs in the lungs where gas exchange occurs due to their large surface area and thin walls.
What is Fick’s Law of Diffusion?
The rate of diffusion is proportional to the surface area and concentration difference, and inversely proportional to the thickness of the gas exchange surface.
What causes asthma?
Chronic inflammation that leads to hyper-responsive smooth muscle contraction, increased airway resistance, and mucus production.
What is COPD?
Chronic Obstructive Pulmonary Disease, a combination of bronchitis and emphysema, causing airflow limitation.
How does emphysema affect gas exchange?
It reduces the surface area available for gas exchange by destroying alveolar walls and fusing adjacent alveoli.
What is ventilation-perfusion mismatching?
It occurs when air (ventilation) and blood flow (perfusion) are not properly balanced, affecting gas exchange efficiency.
How many alveoli are present in the human lungs?
Around 500 million alveoli.
What role do macrophages play in the lungs?
They engulf and destroy inhaled particles and bacteria in the alveoli as a final line of defense.
What is the significance of pulmonary circulation?
It pumps deoxygenated blood from the right ventricle to the lungs for oxygenation and removes carbon dioxide.
